1. Field of the Invention
The present invention relates to a weight adjustment support device for a vehicle seat such as an automotive seat which is capable of adjusting its cushioning property for weight adjustments according to the weights and tastes of occupants of the seat and, more particularly, to improvements relating to U.S. Pat. No. 4,573,657.
2. Description of the Prior Art
In the above mentioned U.S. Pat. No. 4,573,657, there is disclosed a vertical adjustment device for a vehicle seat in which a slight rotation of an operation lever permits adjustments of the cushioning property of the seat according to the weights of occupants of the seat. According to the above application, there are interposed a pair of X-shaped expansion legs between a mounting frame positioned on the side of a vehicle body and a seat support frame on the side of the seat; the two expansion legs are provided therebetween with springs which energize the expansion legs in a direction of sliding of the expansion legs; and, the above-mentioned operation lever is attached to a cam which adjusts the elastic forces of the springs. Thus, by means of operation of the operation lever, the cam can be rotated against the elastic forces of the springs to adjust the elastic forces of the springs so as to obtain the proper cushioning property of the seat according to the weights of the occupants.
As described above, the vertical adjustment device disclosed in the above application is satisfactory as a device using an operation lever. However, there remains still a disadvantage in the above-mentioned vertical adjustment device; that is, a stepless and smooth adjustment of the elastic forces of the springs can not be performed due to the fact that the cam is rotated by means of the operation lever.